Jay Ruby

JRuby is a RubyLanguage interpreter written in JavaLanguage for running on the JavaVirtualMachine

It allows access to the Java classes and libraries when programming in Ruby. You can also invoke the JRuby interpreter from Java.

• http://www.jruby.org/

JRuby 1.0 was released June 12, 2007. It is Ruby version 1.8.5-compatible and provides the vast majority of the usual Ruby standard library. It also comes with RubyGems and RakeMake.

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JRuby with JavaSwing

 #!/usr/bin/env jruby

 # File hello_world_swing.rb (2007-08-13)
 # A translation of Java tutorial HelloWorldSwing.java into JRuby 1.0
 # http://java.sun.com/docs/books/tutorial/uiswing/examples/start/HelloWorldSwingProject/src/start/HelloWorldSwing.java

 require 'java'
 include_class 'javax.swing.JFrame'
 include_class 'javax.swing.JLabel'
 include_class 'javax.swing.SwingUtilities'

 def create_and_show_gui()
   # Create and set up the window
   frame = JFrame.new("Swingin' JRuby")
   frame.set_default_close_operation(JFrame::EXIT_ON_CLOSE)

   # Add the ubiquitous Hello World label
   label = JLabel.new("Hello, JRuby 1.0. How's it swingin'?")
   frame.get_content_pane.add(label)

   # Display the window
   frame.pack
   frame.set_visible(true)
 end

 if $0 == __FILE__
   class HelloRunnable
     # Implement interface by including module
     include java.lang.Runnable

     def run()
       create_and_show_gui
     end
   end

   # Schedule a job for the event-dispatching thread
   # creating and showing this application's GUI
   SwingUtilities.invoke_later(HelloRunnable.new)
 end

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 #!/usr/bin/env jruby

 # File file_system_lister.rb (2007-08-13)
 # Use CLI or JFileChooser to select a directory for file system listing
 # Don't bother loading the Java libraries if we don't need them

 require 'find'

 def list_file_sizes(dir_path)
   puts format('%10s : %s', 'BYTES', 'FILE PATH')
   Find.find(dir_path) do |f|
     puts format('%10d : %s', FileTest.size(f), f) if FileTest.file?(f)
   end
 end

 dir_path = ARGV[0]

 if dir_path.nil?
   require 'java'
   include_class 'javax.swing.JFileChooser'

   chooser = JFileChooser.new  # starts at home directory by default
   chooser.set_file_selection_mode(JFileChooser::DIRECTORIES_ONLY)
   return_val = chooser.show_open_dialog(javax.swing.JPanel.new)

   if return_val == JFileChooser::APPROVE_OPTION
     dir_path = chooser.get_selected_file.get_path
   end
 end

 list_file_sizes(dir_path) unless dir_path.nil?
 exit  # important

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RubyLanguage and JavaLanguage DataStructures

 # Ruby Array <-> Java array
 jArray = rArray.to_java
 rArray = jArray.to_a    # or Array.new(jArray)

 # Ruby Array <-> Java Vector
 jVector = Vector.new rArray
 rArray = jVector.to_a   # Array.new(jVector) won't work

 # Ruby Array of Arrays <-> Java Vector of Vectors
 jVoV = rAoA.inject(Vector.new) { |v, row| v.addElement(Vector.new(row)) ; v }
 rAoA = jVoV.inject([]) { |a, row| a << row.to_a }

 # Ruby Array <-> Java ArrayList
 jArrayList = ArrayList.new rArray
 rArray = jArrayList.to_a

 # Ruby Array <-> Java LinkedList
 jLinkedList = LinkedList.new rArray
 rArray = jLinkedList.to_a

 # Ruby Set <-> Java HashSet
 jHashSet = HashSet.new rSet.to_a
 rSet = Set.new jHashSet

 # Ruby SortedSet <-> Java TreeSet
 jTreeSet = TreeSet.new rSortedSet.to_a
 rSortedSet = SortedSet.new jTreeSet

 # Ruby Hash <-> Java Hashtable (caution, this will remove any nesting)
 jHashtable = Hashtable.new rHash
 rHash = Hash[*jHashtable.to_a.flatten]

 # Ruby Hash <-> Java HashMap (caution, this will remove any nesting)
 jHashMap = HashMap.new rHash
 rHash = Hash[*jHashMap.to_a.flatten]

 # Ruby Hash <-> Java TreeMap
 jTreeMap = TreeMap.new rHash
 rHash = Hash[*jTreeMap.to_a.flatten]

I have yet to figure out how to construct an array of arrays which a Java method accepts as an Object[][] argument. So I look around for an overloaded method which accepts a Vector of Vectors. Does anyone know if JRuby can cobble together something which passes as Object[][]? -- ElizabethWiethoff

 # Generate Object[][] from 2D ruby array:
 [['a', 'b'], ['d', 'e']].to_java(java.lang.Object[])

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CategoryRuby, CategoryJava